Photodetector circuits are utilized in various devices (e.g., focal plane arrays and other photo-sensing circuits) to sense incident light in the visible and non-visible spectra. Many attempts have been made to employ photodetectors to detect the presence of certain agents (e.g., the presence of biological, chemical, and/or hazardous agents). However, the present of certain agents proximate to a photodetector may not significantly affect the intensity of light incident on the photodetector, but instead the peak wavelength(s) of the incident light may shifted. Accordingly, photodetectors suited to detect light intensity are often not practical for use of detecting the presence of agents.